Loudspeakers employing a piezoelectric transducer capable of propagating surface acoustic waves to drive a diaphragm have been proposed as an alternative to moving coil loudspeakers. Such a device was described by Martin in U.S. Pat. No. 4,368,401 and later Takaya in U.S. Pat. No. 4,439,640. Both inventions dealt with attaching a disc shaped piezo to a diaphragm. Martin's device used a thick glue layer (10 to 50% of the carrier plate thickness) between a carrier plate and the piezo ceramic. The adhesive layer served to attenuate resonance. Any displacement in the piezoelectric is directly related to the applied electrical potential.
One disadvantage to utilizing transducers employing a piezoelectric element is that such materials are very costly and that a substantial expense would be involved to utilize a sufficiently sized piezo electric material to drive large diaphragms. Another disadvantage is that piezoelectric materials are as a rule comparatively brittle and do not deform well. Consequently, if one attempts to have piezoelectric materials conform to the curvature of an irregularly shaped diaphragm they may shatter or break, resulting in necessary expense.
Therefore it would be advantageous to attempt to reduce the cost of using piezoelectric elements in a transducer and to adapt them is such a way to a diaphragm so as to reduce the possibility of having the piezo be damaged.